[PEDA] First BGA design with blind-buried vias.

[Richard Sumner]

Brian,

I'm currently debugging a 6 layer board with a 676 pin bga. I 
actually needed only 316 of the i/o pins, and I simply avoided the 
deep rows of the bga. With only 1 trace between bga pads, I can get 
the first two rows (counting from the outside in) on the top layer, 
and using thru vias I can get the next two rows (equivalent, you have 
to avoid blocking the planes with adjacent clearance around the vias) 
on the bottom (or any other layer). This is a low volume product, not 
very (parts) cost sensitive, so I can justify the larger package 
(It's actually a trade off with a more expensive board). It was my 
first board with ad2004, and I did make use of the fpga pin swapping 
(much easier than with 99se, but still not simple)

Richard


At 04:14 PM 6/21/2006, you wrote:
>Ok, I'm still using P99SE.
>
>     I need to upgrade an existing project with the main IC being a 240 QFP,
>going to an Altera 484 pin, 1mm fineline BGA, however, there are some parts
>under the chip.
>
>     My PCB is only 6 layers.  I've never done blind/buried vias before in
>protel.  How should I configure protel to handle the blind-buried vias under
>the BGA pads.  Am I attempting something that shouldn't be done?  Can some
>BGA pads just be pads with no holes at all without upsetting the mounting?
>Is there any good reason to switch to microvias?
>
>
>____________
>Brian G.
>
>
>
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